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		<time class="dt-published" datetime="2020-05-06T00:00:00-04:00" itemprop="datePublished">Wednesday, May 6, 2020
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		<h1 id="0109-sfx--using-bindproperty-to-sync-properties-over-multiple-widgets">0109: SFX – Using bindProperty() to Sync Properties Over Multiple Widgets</h1>

<p>This post is the result of a discussion with Ferhat Kurtulmuş on the <em>D Forum</em>. He pointed out that <code class="language-plaintext highlighter-rouge">bindProperty()</code> can be used to sync up the sensitivity of a bunch of widgets. Change one and they all change. It sounded rather intriguing, so let’s have a look, shall we?</p>

<h2 id="widget-sync">Widget Sync</h2>

<!-- 0, 1 -->
<!-- first occurrence of application and terminal screen shots on a single page -->
<div class="screenshot-frame">
	<div class="frame-header">
		Results of this example:
	</div>
	<div class="frame-screenshot">
		<figure>
			<img id="img0" src="../images/screenshots/016_sfx/sfx_09.png" alt="Current example output" />		<!-- img# -->
			
			<!-- Modal for screenshot -->
			<div id="modal0" class="modal">																	<!-- modal# -->
				<span class="close0">&times;</span>															<!-- close# -->
				<img class="modal-content" id="img00" />															<!-- img## -->
				<div id="caption"></div>
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			img.onclick = function()
			{
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			  modalImg.src = this.src;
			  captionText.innerHTML = this.alt;
			}
			
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			{ 
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			}
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			<figcaption>
			Current example output
			</figcaption>
		</figure>
	</div>

	<div class="frame-terminal">
		<figure class="right">
			<img id="img1" src="../images/screenshots/016_sfx/sfx_09_term.png" alt="Current example terminal output" />		<!-- img#, filename -->

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			<figcaption>
				Current example terminal output (click for enlarged view)
			</figcaption>
		</figure>
	</div>

	<div class="frame-footer">																								<!-- ------------- filename (below) --------- -->
		The code file for this example is available <a href="https://github.com/rontarrant/gtkd_demos/blob/master/016_sfx/sfx_09_bindproperty.d" target="_blank">here</a>.
	</div>
</div>
<!-- end of snippet for first (1st) occurrence of application and terminal screen shots on a single page -->

<p>Looking at the screen-shot, you’ll see a list of three <code class="language-plaintext highlighter-rouge">Switch</code>s and, at the bottom, a single standard <code class="language-plaintext highlighter-rouge">Button</code> that will control their sensitivity. The standard <code class="language-plaintext highlighter-rouge">Button</code> only changes the <code class="language-plaintext highlighter-rouge">"sensitive"</code> flag on the first <code class="language-plaintext highlighter-rouge">Switch</code>. The rest have theirs bound to that of the first. Anyway, let’s have a look at how it works…</p>

<h3 id="adding-companion-widgets">Adding Companion Widgets</h3>

<p>The function that sets all this up is part of the <code class="language-plaintext highlighter-rouge">MyButton</code> class and looks like this:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">void</span> <span class="n">addCompanion</span><span class="p">(</span><span class="n">Widget</span> <span class="n">widget</span><span class="p">)</span>
<span class="p">{</span>
	<span class="n">companions</span> <span class="p">~=</span> <span class="n">widget</span><span class="p">;</span>
		
	<span class="k">if</span><span class="p">(</span><span class="n">companions</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="p">!=</span> <span class="n">widget</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">companions</span><span class="p">[</span><span class="mi">0</span><span class="p">].</span><span class="n">bindProperty</span><span class="p">(</span><span class="s">"sensitive"</span><span class="p">,</span> <span class="n">widget</span><span class="p">,</span> <span class="s">"sensitive"</span><span class="p">,</span> <span class="n">GBindingFlags</span><span class="p">.</span><span class="n">DEFAULT</span><span class="p">);</span>
	<span class="p">}</span>

<span class="p">}</span> <span class="c1">// addCompanion()</span>
</code></pre></div></div>

<p>The <code class="language-plaintext highlighter-rouge">if()</code> statement makes sure the zeroeth <code class="language-plaintext highlighter-rouge">Switch</code> has already been assigned to the <code class="language-plaintext highlighter-rouge">companions</code> array before doing anything. It then names that zeroeth <code class="language-plaintext highlighter-rouge">Switch</code> as the observed <code class="language-plaintext highlighter-rouge">Switch</code>, so to speak, and binds its <code class="language-plaintext highlighter-rouge">sensitive</code> property to any other <code class="language-plaintext highlighter-rouge">Switch</code> widgets passed into the <code class="language-plaintext highlighter-rouge">addCompanion()</code> function.</p>

<p>This example only uses <code class="language-plaintext highlighter-rouge">Switch</code>es, but you can use anything, really, as long as you up-cast to <code class="language-plaintext highlighter-rouge">Widget</code> as you pass it to <code class="language-plaintext highlighter-rouge">addCompanion()</code>.</p>

<h3 id="making-the-list-of-switches-insensitive">Making the List of Switches Insensitive</h3>

<p>This is done in the <code class="language-plaintext highlighter-rouge">onButtonPress()</code> callback:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">bool</span> <span class="n">onButtonPress</span><span class="p">(</span><span class="n">Event</span> <span class="n">e</span><span class="p">,</span> <span class="n">Widget</span> <span class="n">w</span><span class="p">)</span>
<span class="p">{</span>
	<span class="k">if</span><span class="p">(</span><span class="n">companions</span><span class="p">[</span><span class="mi">0</span><span class="p">].</span><span class="n">getSensitive</span><span class="p">()</span> <span class="k">is</span> <span class="kc">false</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="s">"Activating switch"</span><span class="p">);</span>
		<span class="n">companions</span><span class="p">[</span><span class="mi">0</span><span class="p">].</span><span class="n">setSensitive</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
	<span class="p">}</span>
	<span class="k">else</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="s">"Deactivating switch."</span><span class="p">);</span>
		<span class="n">companions</span><span class="p">[</span><span class="mi">0</span><span class="p">].</span><span class="n">setSensitive</span><span class="p">(</span><span class="kc">false</span><span class="p">);</span>
		<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">]);</span>
	<span class="p">}</span>
		
	<span class="k">return</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// onButtonPress()</span>
</code></pre></div></div>

<p>This is pretty much the same as the <code class="language-plaintext highlighter-rouge">onButtonPress()</code> function we saw in the first demo we talked about in <a href="./0104-widget-opacity-ii.html">Blog Post #0104</a>. The only difference is that we’re working with an array of companion widgets instead of just one.</p>

<p>The <code class="language-plaintext highlighter-rouge">MySwitch</code> class is identical, so the only thing left to look at is…</p>

<h3 id="the-buttongrid-constructor">The ButtonGrid Constructor</h3>

<p>And really, all we’re looking at here is how these <code class="language-plaintext highlighter-rouge">Switch</code>es are all stuffed into the UI and associated, each with the first…</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">this</span><span class="p">()</span>
<span class="p">{</span>
	<span class="n">switchLabel1</span> <span class="p">=</span> <span class="k">new</span> <span class="n">Label</span><span class="p">(</span><span class="s">"Insensitize Me"</span><span class="p">);</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">switchLabel1</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
	<span class="n">mySwitch1</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MySwitch</span><span class="p">();</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">mySwitch1</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
		
	<span class="n">switchLabel2</span> <span class="p">=</span> <span class="k">new</span> <span class="n">Label</span><span class="p">(</span><span class="s">"Insensitize Me, too"</span><span class="p">);</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">switchLabel2</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
	<span class="n">mySwitch2</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MySwitch</span><span class="p">();</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">mySwitch2</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
		
	<span class="n">switchLabel3</span> <span class="p">=</span> <span class="k">new</span> <span class="n">Label</span><span class="p">(</span><span class="s">"Me, three!"</span><span class="p">);</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">switchLabel3</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
	<span class="n">mySwitch3</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MySwitch</span><span class="p">();</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">mySwitch3</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>

	<span class="n">myButton</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MyButton</span><span class="p">();</span>
	<span class="n">attach</span><span class="p">(</span><span class="n">myButton</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
	<span class="n">myButton</span><span class="p">.</span><span class="n">addCompanion</span><span class="p">(</span><span class="k">cast</span><span class="p">(</span><span class="n">Widget</span><span class="p">)</span><span class="n">mySwitch1</span><span class="p">);</span>
	<span class="n">myButton</span><span class="p">.</span><span class="n">addCompanion</span><span class="p">(</span><span class="k">cast</span><span class="p">(</span><span class="n">Widget</span><span class="p">)</span><span class="n">mySwitch2</span><span class="p">);</span>
	<span class="n">myButton</span><span class="p">.</span><span class="n">addCompanion</span><span class="p">(</span><span class="k">cast</span><span class="p">(</span><span class="n">Widget</span><span class="p">)</span><span class="n">mySwitch3</span><span class="p">);</span>

	<span class="n">setBorderWidth</span><span class="p">(</span><span class="n">borderWidth</span><span class="p">);</span>
	<span class="n">setMarginBottom</span><span class="p">(</span><span class="mi">10</span><span class="p">);</span>
	<span class="n">setColumnSpacing</span><span class="p">(</span><span class="n">columnSpacing</span><span class="p">);</span>
	<span class="n">setRowSpacing</span><span class="p">(</span><span class="n">rowSpacing</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// this()</span>
</code></pre></div></div>

<p>The first three sets of four statements each add a <code class="language-plaintext highlighter-rouge">Switch</code> along with a <code class="language-plaintext highlighter-rouge">Label</code>. The only tricky bit in there is making sure we count <code class="language-plaintext highlighter-rouge">Grid</code> rows and columns correctly. That’s something that, I’m sure, could be automated if one put some effort into it. Perhaps that’ll be the subject of a future post. Anyway…</p>

<p>Once we add <code class="language-plaintext highlighter-rouge">myButton</code>—the standard <code class="language-plaintext highlighter-rouge">Button</code> that triggers all this insensitivity—we drop it onto the <code class="language-plaintext highlighter-rouge">Grid</code> and then call <code class="language-plaintext highlighter-rouge">myButton.addCompanion()</code> for each <code class="language-plaintext highlighter-rouge">Switch</code>.</p>

<p>The rest is all stuff we’ve done before.</p>

<h2 id="conclusion">Conclusion</h2>

<p>There’s no limit to how many <code class="language-plaintext highlighter-rouge">Widgets</code>—or which type(s) of <code class="language-plaintext highlighter-rouge">Widgets</code>—we can add to the list. Since <code class="language-plaintext highlighter-rouge">addCompanion()</code> is set up to add a generic <code class="language-plaintext highlighter-rouge">Widget</code>, all you have to do is use the <code class="language-plaintext highlighter-rouge">cast()</code> function to match what <code class="language-plaintext highlighter-rouge">addCompanion()</code> needs and you’re all set. And with <code class="language-plaintext highlighter-rouge">ObjectG</code> being everybody’s great-grandparental unit, you don’t have to worry about climbing too far up the hierarchy to access the <code class="language-plaintext highlighter-rouge">bindProperty()</code> function.</p>

<p>That’s it for now. Take care of each other and don’t let the bad guys win.</p>

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        <p>Simple examples of how to use GtkD to build GUI applications.</p>
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